Within the field of shaping technology many possibilities are known for shaping metal strips into profiles. “Roll forming”, sometimes also termed “roller profiling”, is particularly well-suited to continuous, progressive shaping. This is a shaping method in which rotatably mounted tools, for example rolls or rollers, shape the metal strip into profiles. To that end, the rotatably mounted tools are usually arranged in a fixed position while the metal strips to be shaped are continuously moved through the rollers. During the movement of the metal strips, the rotatably mounted and driven tools roll on the metal strips and deform the metal strips by pressing against one another. Often, multiple stations with different-shaped tools are arranged in series such that the metal strips are shaped step-by-step until the desired final cross-section is reached. Roll forming is particularly well-suited to the production of profiles having constant cross sections.
In comparison to other shaping methods (e.g. pressing), roll forming generates relatively high shaping pressures only locally. A great advantage of roll forming lies in the possibility of continuously shaping the metal strips. A further advantage is a high reproducibility of the results. Against this backdrop, the use of roll forming, in particular for the production of large numbers of identical components, is to be considered advantageous, for example for bodywork parts for motor vehicles.
Apparatuses and methods for roll forming are known for example from DE 10 2007 005 880 B4, DE 197 54 171 A1 and DE 100 11 755 A1. With some of the apparatuses and methods described therein, it is possible to generate by roll forming metal strips whose cross sections vary along their longitudinal axis. This is for example achieved by changing or adjusting the position of the tools in the lateral direction during the shaping procedure. In particular, the tools can not only rotate but also execute lateral translational movements. The changing cross sections make it possible for components produced therefrom to be adapted to the loads prevailing in operation.
The known solutions have the disadvantage that great expenditure in terms of machinery is required in order to make the tools—for example a roller set—laterally displaceable. In addition, displaceably mounted tools require a complex control which ensures that the tools always adopt the correct position. A further drawback lies in the fact that only displacing the tools permits only a limited variation in the workpiece geometry or profile geometry.
Another possibility for producing workpieces or profiles having a longitudinally varying cross section by roll forming is known from JP 59 027 722 A. That document proposes, instead of changing the position of the tools, using rotatably mounted tools whose contours are not axially symmetric. In this manner, the metal strips are deformed such that the shape of the metal strips after the shaping procedure approximately corresponds to the shape of the contours of the tools. To that end, two rollers with matching contours and parallel axes of rotation are employed against one another, between which rollers the metal strip is guided and shaped.
Although this solution is simpler in terms of construction, it does have the drawback that the described tools, whose axes of rotation are parallel to one another, do not make it possible to generate hollow profiles, but rather only open profiles or half-shells, and in order to produce hollow profiles two or more half-shells must be joined together. This in turn increases production costs. A further drawback of the solution known from JP 59 027 722 A lies in the fact that, in order to form the open profiles, two tools having different contours are used (a convex “punch” and a concave “die”). This also leads to higher tooling costs.